The present invention relates to a vaporized fuel purge controller for an engine that purges vaporized fuel, which is produced in a fuel tank and adsorbed in a canister, into an intake passage of the engine.
Japanese Laid-Opened Patent Publication No. 6-93900 describes a first prior art example of a vaporized fuel purge controller. In the first prior art example, the purged amount of the vaporized fuel is adjusted by changing the duty ratio of a drive signal, which drives a purge valve arranged between a canister and an intake passage. The duty ratio is calculated in accordance with characteristics of the purge valve.
When the drive voltage of the purge valve decreases in the duty-controlled purge valve, the amount that the purge valve opens relative to the duty ratio changes. In this case, the same flow rate of vaporized fuel may not be obtained even though the purge valve is controlled with the same duty ratio.
When there is a delay in the timing in which the purge valve is opened, a compensation duty ratio is added to the basic duty ratio to compensate for the delay. The purge valve drive voltage (battery voltage) and temperature are referred to when determining the compensation duty ratio. The compensation duty ratio increases as the purge valve drive voltage (battery voltage) decreases and increases as the temperature of the purge valve increases.
FIG. 8 is a graph used to calculate the duty ratio of the drive signal from the target flow rate ratio of the purged gas. The duty signal is sent to the purge valve to duty-control the purge valve. The ideal duty characteristic of the purge valve would be plotted along line La having a slope of 1 in which the duty ratio is 100% (purge valve being fully opened) when the target purged gas flow rate ratio is 100%.
However, electric response delays occur in the actual purge valve. This produces an invalid activation time (valve opening delay) from when the purge valve is activated to when the purge valve starts to open. Thus, the target purged gas flow rate ratio is not achieved even when the purge valve is driven under a duty ratio that is in the vicinity of 0%. Accordingly, in the prior art, a predetermined minimum duty ratio is set. Line Lb1, which is shown in FIG. 8, is used so that a duty ratio that is lower than the minimum duty ratio is not used. In line Lb1, the duty ratio is 0% when the invalid activation time ends.
In this specification, the term xe2x80x9cpurging ratexe2x80x9d refers to the percentage (%) of the amount of purged gas relative to the amount of intake air flowing through the intake passage. The term xe2x80x9cvapor concentrationxe2x80x9d refers to the percentage (%) of the vaporized fuel included in the purged gas when the purging rate is 1%. The term xe2x80x9ctarget purged gas flow rate ratioxe2x80x9d refers to the percentage (%) of the target purged gas flow rate relative to the flow rate of the purged gas when the purge valve is fully opened.
In an engine provided with a vaporized fuel purge controller, changes in the operating conditions of the engine, such as intake pressure, affects the linearity of the relationship between the target purged gas flow rate ratio and the duty ratio. When the linearity of the relationship is lost, the actual purged gas flow rate does not match the target purged gas flow rate. This has an undesirable influence on the purge control air-fuel ratio control.
Referring to FIG. 9, when there is a change in an operating condition of the engine, such as the intake pressure, the duty ratio and the purged gas flow rate ratio (purged gas flow rate/purged gas flow rate when purge valve is fully opened) deviate from their targets (curves Lb2 and Lb3). Due to such a decrease in the flow rate linearity, even if the purge valve is driven using the target duty ratio that is determined in correspondence with the target purged gas flow amount, a purged gas flow rate corresponding to the target duty ratio is not obtained. As a result, the requirements of various types of controls in the engine are not satisfied (i.e., purge control capability decreases). Further, the actual purged gas flow rate deviates from the flow rate that is expected from the target duty ratio. Thus, the vapor concentration that is expected by analysis deviates from the actual vapor concentration. As a result, the actual purged gas flow rate is not accurately predicted and the air-fuel ratio control capability decreases.
This problem is more prominent when employing a purge valve having a valve body that closes the purge valve with a larger force as the intake pressure decreases (as the intake negative pressure increases). Such a purge valve has a characteristic in which it becomes difficult to close the valve at low duty ratios as the difference between the intake pressure (i.e., the pressure at a location immediately downstream of the purge valve) and the atmospheric pressure (i.e., the pressure at a location immediately upstream of the purge valve) increases. Due to this characteristic, it becomes difficult to obtain a purged gas flow rate corresponding to the duty ratio. This tendency becomes prominent when the drive voltage decreases.
The above problem also occurs when employing an electromagnetic valve (hereafter referred to as solenoid type purge valve) that is controlled in accordance with the current value of the drive signal. This is because a change in the intake pressure causes the actual opened amount of the purge valve to deviate from the target opened amount.
The deviation of the duty ratio from the flow rate ratio (i.e., decrease in the flow rate linearity), which results from changes in the operating condition of the engine, also occurs when employing a duty control type purge valve or solenoid type purge valve. These valves have a characteristic in which the opened amount of the purge valve increases as the negative intake pressure increases. In each valve, as the negative intake pressure increases, a force that is applied to the valve body in a direction closing the valve decreases.
Further, in the first prior art example, due to electric response delays when activating or deactivating the purge valve, the relationship between the purged gas flow rate ratio and the duty ratio is as shown by curve Lb4 in FIG. 10. Changes in the purged gas flow rate ratio decreases when the duty ratio is in the proximity of 0%, and changes in the purged gas flow rate ratio increases when the duty ratio is in the proximity of 100%. Thus, even if the influence of the invalid activation time is corrected, the actual purged gas flow rate cannot be accurately calculated based on the ideal line La. As a result, the fuel injection amount cannot be accurately corrected. This has an undesirable effect on air-fuel ratio control.
Japanese Laid-Opened Patent Publication 2000-27718 describes a second prior art example. In the second prior art example, the opened amount of the purge valve is determined by referring to an interpolation value map generated from the intake pressure and the target purged gas flow rate. In the map, the set opened amount of the purge valve decreases as the intake pressure decreases (i.e., negative pressure increases), and the set opened amount of the purge valve also decreases as the target purged gas flow rate decreases. However, as the intake pressure decreases, it becomes difficult for the purge valve closed by negative pressure to open at a low duty ratio. Thus, in the second prior art example, when using such a purge valve, the target purged gas flow rate corresponding to the duty ratio cannot be achieved.
It is an object of the present invention to provide a vaporized fuel purge controller for an engine that facilitates purge control and air-fuel ratio control and improves drivability.
To achieve the above object, the present invention provides a purge controller for controlling a vaporized fuel processing mechanism in an engine. The vaporized fuel processing mechanism has a canister and a purge valve for controlling flow of purged gas, which includes air and vaporized fuel adsorbed by the canister, into an intake system of the engine. The engine undergoes purge control and air-fuel ratio control, and the purge valve is driven in accordance with the level of a drive signal. The purge controller includes a target level calculating means for calculating a target level of the drive signal. The target level calculating means uses a parameter representing the operating condition of the engine and a predetermined flow rate ratio of purged gas to presume the deviation between the purged gas flow rate ratio and the level of the drive signal that results from a characteristic of the purge valve and calculates the target level in accordance with the presumed deviation.
A further aspect of the present invention is a purge controller for controlling a vaporized fuel processing mechanism of an engine that has an intake passage and undergoes air-fuel control. The vaporized fuel processing mechanism has a purge valve to introduce into the intake passage a controlled amount of purged gas, which includes air and the vaporized fuel, and the purge valve is driven in accordance with the level of a drive signal. The controller includes a sensor for detecting an operating condition of the engine and a computer for calculating a level of the drive signal. The computer presumes a fully opened flow rate of the purged gas introduced into the intake passage which is the purged gas flow rate when the purge valve is fully opened during the present engine operating condition detected by the sensor. The computer also calculates a ratio between the presumed fully opened flow rate and a target flow rate designated by the air-fuel control. Further, the computer calculates the level of the drive signal based on the ratio and the present engine operating condition.
A further aspect of the present invention is a purge control method for controlling a vaporized fuel processing mechanism of an engine that has an intake passage and undergoes air-fuel control. The vaporized fuel processing mechanism has a purge valve to introduce into the intake passage a controlled amount of purged gas, which includes air and vaporized fuel. The purge valve is driven in accordance with the level of a drive signal. The method includes detecting a present operating condition of the engine, presuming a fully opened flow rate of the purged gas introduced into the intake passage, which is the purged gas flow rate when the purge valve is fully opened during the present engine operating condition, calculating a ratio between the presumed fully opened flow rate and a target flow rate designated through the air-fuel control, calculating a level of the drive signal from the ratio and the present engine operating condition, and providing the purge valve with drive signal having the calculated level.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.